Service Function Chaining (SFC) Control Plane Components & Requirements
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|Authors||Hongyu Li , Qin Wu , Oliver Huang , Mohamed Boucadair , Christian Jacquenet , Walter Haeffner , Seungik Lee , Ron Parker , Linda Dunbar , Andrew G. Malis , Joel M. Halpern , Tirumaleswar Reddy.K , Prashanth Patil|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||I-D Exists|
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Service Function Chaining (sfc) H. Li Internet-Draft Q. Wu Intended status: Informational O. Huang Expires: February 29, 2016 Huawei M. Boucadair, Ed. C. Jacquenet France Telecom W. Haeffner Vodafone S. Lee ETRI R. Parker Affirmed Networks L. Dunbar A. Malis Huawei Technologies J. Halpern Ericsson T. Reddy P. Patil Cisco August 28, 2015 Service Function Chaining (SFC) Control Plane Components & Requirements draft-ietf-sfc-control-plane-00 Abstract This document describes requirements for conveying information between Service Function Chaining (SFC) control elements (including management components) and SFC functional elements. Also, this document identifies a set of control interfaces to interact with SFC- aware elements to establish, maintain or recover service function chains. This document does not specify protocols nor extensions to existing protocols. This document exclusively focuses on SFC deployments that are under the responsibility of a single administrative entity. Inter-domain considerations are out of scope. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute Li, et al. Expires February 29, 2016 [Page 1] Internet-Draft SFC Control Plane August 2015 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on February 29, 2016. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 5 2. Generic Considerations . . . . . . . . . . . . . . . . . . . 6 2.1. Generic Requirements . . . . . . . . . . . . . . . . . . 6 2.2. SFC Control Plane Bootstrapping . . . . . . . . . . . . . 6 2.3. Coherent Setup of an SFC-enabled Domain . . . . . . . . . 7 3. SFC Control Plane: Reference Architecture & Interfaces . . . 8 3.1. Reference Architecture . . . . . . . . . . . . . . . . . 8 3.2. Centralized vs. Distributed . . . . . . . . . . . . . . . 9 3.3. Interface Reference Points . . . . . . . . . . . . . . . 10 3.3.1. C1: Interface between SFC Control Plane & SFC Classifier . . . . . . . . . . . . . . . . . . . . . 10 3.3.2. C2: Interface between SFC Control Plane & SFF . . . . 12 3.3.3. C3: Interface between SFC Control Plane & SFC-aware SFs . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.3.4. C4: Interface between SFC Control Plane & SFC Proxy . 13 4. Additional Considerations . . . . . . . . . . . . . . . . . . 14 4.1. Discovery of the SFC Control Element . . . . . . . . . . 14 4.2. SF Symmetry . . . . . . . . . . . . . . . . . . . . . . . 14 Li, et al. Expires February 29, 2016 [Page 2] Internet-Draft SFC Control Plane August 2015 4.3. Pre-deploying SFCs . . . . . . . . . . . . . . . . . . . 14 4.4. Withraw a Service Function (SF) . . . . . . . . . . . . . 14 4.5. SFC/SFP Operations . . . . . . . . . . . . . . . . . . . 15 4.6. Unsolicited (Notification) Messages . . . . . . . . . . . 15 4.7. SF Liveness Detection . . . . . . . . . . . . . . . . . . 15 4.8. Monitoring & Counters . . . . . . . . . . . . . . . . . . 16 4.9. Validity Lifetime . . . . . . . . . . . . . . . . . . . . 16 4.10. Considerations Specific to the Centralized Path Computation Model . . . . . . . . . . . . . . . . . . . . 16 4.10.1. Service Function Path Adjustment . . . . . . . . . . 17 4.10.2. Head End Initiated SFP Establishment . . . . . . . . 17 4.10.3. (Regional) Restoration of Service Functions . . . . 18 5. Security Considerations . . . . . . . . . . . . . . . . . . . 18 5.1. Secure Communications . . . . . . . . . . . . . . . . . . 18 5.2. Pervasive Monitoring . . . . . . . . . . . . . . . . . . 19 5.3. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.4. Denial-of-Service (DoS) . . . . . . . . . . . . . . . . . 19 5.5. Illegitimate Discovery of SFs and SFC Control Elements . 20 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.1. Normative References . . . . . . . . . . . . . . . . . . 20 7.2. Informative References . . . . . . . . . . . . . . . . . 20 Appendix A. RSP-related Considerations . . . . . . . . . . . . . 22 A.1. Encoding the Exact SFF-SF-sequence in Data Packets . . . 22 A.2. Fully Controlled SFF-SF-Sequence for a SFP . . . . . . . 22 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 23 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 1. Introduction The dynamic enforcement of a service-derived forwarding policy for packets entering a network that supports advanced Service Functions (SFs) has become a key challenge for operators. Typically, many advanced Service Functions (e.g., Performance Enhancement Proxies ([RFC3135]), NATs [RFC3022][RFC6333][RFC6146], firewalls [I-D.ietf-opsawg-firewalls], etc.) are solicited for the delivery of value-added services, particularly to meet various service objectives such as IP address sharing, avoiding covert channels, detecting and protecting against ever increasing Denial-of-Service (DoS) attacks, etc. Because of the proliferation of such advanced service functions together with complex service deployment constraints that demand more agile service delivery procedures, operators need to rationalize their service delivery logics and master their complexity while optimising service activation time cycles. The overall problem space is described in [RFC7498]. A more in-depth discussion on use cases Li, et al. Expires February 29, 2016 [Page 3] Internet-Draft SFC Control Plane August 2015 can be found in [I-D.ietf-sfc-use-case-mobility] and [I-D.ietf-sfc-dc-use-cases]. [I-D.ietf-sfc-architecture] presents a model addressing the problematic aspects of existing service deployments, including topological dependence and configuration complexity. It also describes an architecture for the specification, creation, and ongoing maintenance of Service Function Chains (SFC) within a network. That is, how to define an ordered set of Service Functions and ordering constraints that must be applied to packets and/or frames and/or flows selected as a result of classification. 1.1. Scope While [I-D.ietf-sfc-architecture] focuses on data plane considerations, this document describes requirements for conveying information between SFC control elements (including management components) and SFC functional elements. Also, this document identifies a set of control interfaces to interact with SFC-aware elements to establish, maintain or recover service function chains. Both distributed and centralized control plane schemes to install SFC-related state and influence forwarding policies are discussed. This document does not make any assumption on the deployment use cases. In particular, the document implicitly covers fixed, mobile, data center networks and any combination thereof. This document does not make any assumption about which control protocol to use, whether one or multiple control protocols are required, or whether the same or distinct control protocols will be invoked for each of the control interfaces. It is out of scope of this document to specify a profile for an existing protocol, to define protocol extensions, or to select a protocol. Considerations related to the chaining of Service Functions that span domains owned by multiple administrative entities are out of scope. It is out of scope of this document to discuss SF-specific control and policy enforcement schemes; only SFC considerations are elaborated, regardless of the various connectivity services that may be supported in the SFC domain. Likewise, only the control of SFC- aware elements is discussed. Service catalogue (including guidelines for deriving service function chains) is out of scope. Li, et al. Expires February 29, 2016 [Page 4] Internet-Draft SFC Control Plane August 2015 1.2. Terminology The reader should be familiar with the terms defined in [RFC7498] and [I-D.ietf-sfc-architecture]. The document makes use of the following terms: o SFC data plane functional element: Refers to SFC-aware Service Function, Service Function Forwarder (SFF), SFC Proxy, or SFC Classifier as defined in the SFC data plane architecture [I-D.ietf-sfc-architecture]. o SFC Control Element: A logical entity that instructs one or more SFC data plane functional elements on how to process packets within an SFC-enabled domain. o SFC Classification entry: Refers to an entry maintained by an SFC Classifier that reflects the policies for binding an incoming flow/packet to a given SFC. Actions are associated with matching criteria. For example, packets can be marked with the appropriate SFC-related information to differentiate flows so that subsequent SFFs can forward the flows to a sequence of SFs in a given order. The set of classification entries maintained by a Classifier are referred to as in the classification policy table. o SFC Forwarding Policy Table: this table reflects the SFC-specific traffic forwarding policy enforced by SFF components for every relevant incoming packet that is associated to one of the existing SFCs. [[Note: The question of whether the data plane operates just in terms of SFP IDs or needs SFC IDs, as described in this version of the draft, is still under discussion among the authors.]] 1.3. Assumptions This document adheres to the assumptions listed in Section 1.2 of [I-D.ietf-sfc-architecture]. This document does not make any assumptions about the co-location of SFC data plane functional elements; this is deployment-specific. This document can accommodate a variety of deployment contexts such as (but not limited to): o A Service Function Forwarder (SFF) can connect instances of the same or distinct SFs. o A SF instance can be serviced by one or multiple SFFs. o One or multiple SFs can be co-located with a SFF. o A boundary node (that connects one SFC-enabled domain to a node either located in another SFC-enabled domain or in a domain that Li, et al. Expires February 29, 2016 [Page 5] Internet-Draft SFC Control Plane August 2015 is SFC-unaware) can act as an egress node and an ingress node for the same flow. o Distinct ingress and egress nodes may be crossed by a packet when forwarded in an SFC-enabled domain. o Distinct ingress nodes may be solicited for each traffic direction (e.g., upstream and downstream). o An ingress node can embed a Classifier. o An ingress node may not embed a Classifier, but it can be responsible for dispatching flows among a set of Classifiers. o The same boundary node may act as an ingress node, an egress node, and also embed a Classifier. o A Classifier can be hosted in a node that embeds one or more SFs. o Many network elements within an SFC-enabled domain may behave as egress/ingress nodes. Furthermore, the following assumptions are made: o A Control Element can be co-located with a Classifier, SFF or SF. o One or multiple Control Elements can be deployed in an SFC-enabled domain. o State synchronization between Control Elements is out of scope. 2. Generic Considerations 2.1. Generic Requirements For deployments that would require so, SFC forwarding must be allowed even if no control protocols are enabled. Static configuration must be allowed. A permanent association between an SFC data plane element with a Control Element must not be required; specifically, the SFC-enabled domain must keep on processing incoming packets according to the SFC instructions even during temporary unavailability events of control plane components. SFC implementations that do not meet this requirement will suffer from another flavor of the constrained high availability issue, discussed in Section 2.3 of [RFC7498], supposed to be solved by SFC designs. 2.2. SFC Control Plane Bootstrapping The interface that is used to feed the SFC control plane with service objectives and guidelines is not part of the SFC control plane itself. Therefore, this document assumes the SFC control plane is provided with a set of information that is required for proper SFC operation with no specific assumption about how this information is collected/provisioned, nor about the structure of such information. Li, et al. Expires February 29, 2016 [Page 6] Internet-Draft SFC Control Plane August 2015 The following information that is likely to be provided to the SFC control plane at bootstrapping includes (non-exhaustive list): o Locators for Classifiers/SFF/SFs/Proxies, etc. o SFs serviced by each SFF. o A list of service function chains, including how they are structured and unambiguously identified. o Status of each SFC: active/pre-deployment phase/etc. A SFC can be defined at the management level and instantiated in an SFC-enabled domain for pre-deployment purposes (e.g., testing). Actions to activate, modify or withdraw an SFC are triggered by the control plane. Nevertheless, this document does not make any assumption about how an operator instructs the control plane. o A list of classification guidelines and/or rules to bind flows to SFCs/SFPs. o Optionally, (traffic/CPU/memory) load balancing objectives at the SFC level or on a per node (e.g., per-SF/SFF/Proxy) basis. o Security credentials. o Context information that needs to be shared on a per SFC basis. Also, the SFC control plane may gather the following information from an SFC-enabled domain at bootstrapping (non-exhaustive list). How this information is collected is left unspecified in this document: o The list of active SFC-aware SFs (including their locators). o The list of SFFs and the SFs that are attached to. o The list of enabled SFC Proxies, and the list of SFC-unware SFs attached to. o The list of active SFCs/SFPs as enabled in an SFC-enabled domain. o The list of Classifiers and their locators, so as to retrieve the classification policy table for each Classifier, in particular. o The SFC forwarding policy tables maintained by SFFs. During the bootstrapping phase, a Control Element may detect a conflict between the running configuration in an SFC data plane element and the information maintained by the control plane. Consequently, the control plane undertakes appropriate actions to fix those conflicts. This is typically achieved by invoking one of the interfaces defined in Section 3.3. 2.3. Coherent Setup of an SFC-enabled Domain Various transport encapsulation schemes and/or variations of SFC header implementations may be supported by one or several nodes of an SFC-enabled domain. For the sake of coherent configuration, the SFC control plane is responsible for instructing all the involved SFC data plane functional elements about the behavior to adopt to select Li, et al. Expires February 29, 2016 [Page 7] Internet-Draft SFC Control Plane August 2015 the transport encapsulation scheme(s), the version of the SFC header to enable, etc. 3. SFC Control Plane: Reference Architecture & Interfaces 3.1. Reference Architecture The SFC control plane is responsible for the following: o Build and monitor the service-aware topology. For example, this can be achieved by means of dynamic SF discovery techniques. Those means are out of scope of this document. o Maintain a repository of service function chains, SFC matching criteria to bind flows to a given service function chain, and mapping between service function chains and SFPs. o Guarantee the coherency of the configuration and the operation of an SFC-enabled domain. o Dynamically compute a service-aware forwarding path (distributed model, see Section 3.2) o Determine a forwarding path in the context of a centralized deployment model (see Section 3.2). o Update service function chains or adjust SFPs (e.g., for restoration purposes) based on various inputs (e.g., external policy context, path alteration, SF unavailability, SF withdrawal, service decommissioning, etc.). o Populate SFC forwarding policy tables of involved SFC data plane elements and provides Classifiers with traffic classification rules. Figure 1 shows the overall SFC control plane architecture, including interface reference points. This document does not elaborate on the internal decomposition of the SFC Control & Management Plane functional blocks. The components within the SFC Control & Management Planes and their interactions are out of scope. As discussed in Section 3.2, the SFC control plane can be implemented in a (logically) centralized or distributed fashion. Li, et al. Expires February 29, 2016 [Page 8] Internet-Draft SFC Control Plane August 2015 +----------------------------------------------+ | | | SFC Control & Management Planes | +-------| | | | | C1 +------^-----------^-------------^-------------+ +---------------------|C3---------|-------------|-------------+ | | +----+ | | | | | | SF | |C2 |C2 | | | +----+ | | | | +----V--- --+ | | | | | | SFC | +----+ +-|--+ +----+ | | |Classifier |---->|SFF |----->|SFF |------->|SFF | | | | Node |<----| |<-----| |<-------| | | | +-----------+ +----+ +----+ +----+ | | | | | | | |C2 ------- | | | | | | +-----------+ C4 | | V +----+ +----+ | SFC Proxy |--> | | | SF | |SF | +-----------+ | | +----+ +----+ | | |C3 |C3 | | SFC Data Plane Components V V | +-------------------------------------------------------------+ Figure 1: SFC Control Plane: Overview Note, the SFC control plane must be able to invoke SFC OAM mechanisms, and to determine the results of OAM operations. 3.2. Centralized vs. Distributed The SFC control plane can be (logically) centralized, distributed or a combination thereof. Whether one or multiple SFC Control Elements are enabled is deployment-specific. Nevertheless, the following comments can be made: SFC management (including SFC monitoring and supervision): is likely to be centralized. SFC Mapping Rules: i.e., service instructions to bind a flow to a service function chain are likely to be managed by a central SFC Control Element, but the resulting policies can be shared among several Control Elements. Note, these policies can be complemented with local information (e.g., an IPv4 address/IPv6 prefix assigned to a customer) because such information may not be available to the central entity but known only during network attachment phase. Li, et al. Expires February 29, 2016 [Page 9] Internet-Draft SFC Control Plane August 2015 Path computation: can be either distributed or centralized. Distributed path computation means that the selection of the exact sequence of SF functions that a packet needs to invoke (along with instances and/or SFF locator information) is a result of a distributed path selection algorithm executed by involved nodes. For some traffic engineering proposes, the SFP may be constrained by the control plane; as such, some SFPs can be fully specified (i.e., list all the SFF/SFs that need to be solicited) or partially specified (e.g., exclude some nodes, explicitly select which instance of a given SF needs to be invoked, etc.). SFC Resiliency (including restoration) refers to mechanisms to ensure high available service function chains. It includes means to detect node/link/path failures. Both centralized and distributed mechanism to ensure SFC resiliency can be envisaged. Implementing a (logically) centralized path computation engine requires information to be dynamically communicated to the central SFC Control Element, such as the list of available SF instances, SFF locators, load status, SFP availability, etc. 3.3. Interface Reference Points The following sub-sections describe the interfaces between the SFC Control & Management Planes, as well as various SFC data plane elements. 3.3.1. C1: Interface between SFC Control Plane & SFC Classifier As a reminder, a Classifier is a function that is responsible for classifying traffic based on (pre-defined) rules. This interface is used to install SFC classification rules in Classifiers. Once classification rules are populated, SFC Classifiers are responsible for binding incoming traffic to service function chains according to these classification rules. Note, the SFC control plane must not make any assumption on how the traffic is to be bound to a given SFC. In other words, classification rules are deployment-specific. For instance, classification can rely on a subset of the information carried in a received packet such as 5-tuple classification, be subscriber-aware, be driven by traffic engineering considerations, or any combination thereof. The SFC control plane should be responsible for removing invalid (and stale) mappings from the classification tables maintained by the classifiers. Also, local sanity checks mechanisms may be supported locally by the Classifiers, but those are out of scope. Li, et al. Expires February 29, 2016 [Page 10] Internet-Draft SFC Control Plane August 2015 The Classifier may be notified by the control plane about the available SFs (including their locators) or be part of the service function discovery procedure. Classification rules may be updated, deleted or disabled by the control plane. Criteria that would trigger those operations are deployment-specific. Given that service function chaining solutions may be applied to very large sets of traffic, any control solution should take scaling issues into consideration as part of the design. Below are listed some functional objectives for this interface: o Rationalize the management of classification rules. o Maintain a global view of instantiated rules in all Classifiers in an SFC-enabled domain. o Check the consistency of instantiated classification rules within the same Classifier or among multiple Classifier. o Assess the impact of removing or modifying a classification entry on packets entering an SFC-enabled domain. o Aggregate classification rules for the sake of performance optimization (mainly reduce lookup delays). o Adjust classification rules when rules are based on volatile identifiers (e.g., an IPv4 address, IPv6 prefix). o Allow to rapidly restore SFC states during failure events that occurred at a Classifier (or a Control Element). The control plane must instruct the Classifier whether it can trust an existing SFC marking of an incoming packet or whether it must be ignored. For bidirectional packet processing purposes (e.g., full or partial path symmetry), the control plane invokes this interface to configure the appropriate classification entries. A Classifier can send unsolicited messages through this interface to notify the SFC Control & Management Planes about specific events. When re-classification is allowed in an SFC-enabled domain, this interface can be used to control Classifiers co-resident with SFC- aware SFs, SFC Proxies, or SFFs to manage re-classification rules . SFC Classification policy entry should be bound to one single service function chain (or one single SFP); when an incoming packet matches more than one classification entry, tie-breaking criteria should be specified (e.g., priority). Such tie-breaking criteria should be instructed by the control plane. Li, et al. Expires February 29, 2016 [Page 11] Internet-Draft SFC Control Plane August 2015 The identification of instantiated SFCs/SFPs is local to each administrative domain; it is policy-based and deployment-specific. 3.3.2. C2: Interface between SFC Control Plane & SFF SFFs make traffic forwarding decisions according to the entries maintained in their SFC forwarding policy table. Such table is populated by the SFC control plane through the C2 interface. This interface is used to instruct a SFF about the SFC-aware SFs that it can service. This interface is also used by the SFF to report the connectivity to their attached (including embedded) SFs. Local means may be enabled between the SFC-aware SFs and SFFs to allow for the dynamic attachment of SFs to a SFF and/or discovery of SFs by a SFF but those means are unspecified in this document. The C2 interface is also used for collecting states of attributes (e.g., availability, workload, latency), for example, to dynamically adjust Service Function Paths. 3.3.3. C3: Interface between SFC Control Plane & SFC-aware SFs The SFC control plane uses this interface to interact with SFC-aware SFs. SFs may need to output some processing results of packets to the SFC control plane. This information can be used by the SFC control plane to update the SFC classification rules and the SFC forwarding policy table entries. This Interface is used to collect such kind of feedback information from SFs. For example, the following information can be exchanged between a SF and the SFC control plane: o SF execution status: Some SFs may need to send information to the control plane to fine tune SFPs. For example, a threat-detecting SF can periodically send the threat characteristics via this interface, such as high probability of threat with packet of a given size. The control plane can then add an appropriate matching criteria to SFF to steer traffic to a scrubbing center. o SF load update: When SFs are under stress that yielded the crossing of some performance thresholds, the SFC control plane needs to be notified to adjust SFPs accordingly (especially when the centralized path computation mode is enabled). It is out of scope of this document to specify the exact methods to monitor the performance threshold or stress level of SFs, nevertheless the SFC control plane can invoke those methods for its operations. Li, et al. Expires February 29, 2016 [Page 12] Internet-Draft SFC Control Plane August 2015 The SFC control needs the above status information for various tasks it undertakes, but this information may be acquired directly from SFs or indirectly from other management and control systems in the operational environment. This interface is also used to instruct an SFC-aware SF about any context information it needs to supply in the context of a given SFC. Also, this interface informs the SFC-aware SF about the semantics of a context information, which would otherwise have opaque meaning. Several attributes may be associated with a context information such as (but not limited to) the "scope" (e.g., per-packet, per-flow or per host), whether it is "mandatory" or "optional" to process flows bound to a given chain, etc. Note that a context may be mandatory for "chain 1", but optional for "chain 2". The control plane may indicate, for a given service function chain, an order for consuming a set of contexts supplied in a packet. A SFC-aware SF can also be instructed about the behavior is should adopt after consuming a context information that was supplied in the SFC header. For example, the context can be maintained or stripped. The SFC-aware SF can be instructed to inject a new context header into the SFC header. Multiple SFs may be located within the same physical node, and no SFF is enabled in that same node, means to unambiguously forward the traffic to the appropriate SF must be supported. An SF can be instructed to strip the SFC information for the chains it terminates. 3.3.4. C4: Interface between SFC Control Plane & SFC Proxy The SFC control plane uses this interface to interact with an SFC Proxy. The SFC proxy can be instructed about authorized SFC-unware SFs it can service. A SFC Proxy can be instructed about the behavior it should adopt to process the context information that was supplied in the SFC header on behalf of a SFC-unware SF, e.g., the context can be maintained or stripped. The SFC proxy is also instructed about the semantics of a context information, which would otherwise have opaque meaning. Several attributes may be associated with a context information such as (but not limited to) the "scope" (e.g., per-packet, per-flow or per host), Li, et al. Expires February 29, 2016 [Page 13] Internet-Draft SFC Control Plane August 2015 whether it is "mandatory" or "optional" to process flows bound to a given chain, etc. The SFC Proxy can also be instructed to add SF some new context information into the SFC header on behalf of a SFC-unaware SF. The C4 interface is also used for collecting attribute states (e.g., availability, workload, latency), for example, to dynamically adjust Service Function Paths. 4. Additional Considerations 4.1. Discovery of the SFC Control Element SFC data plane functional elements need to be provisioned with the locators of the Control Elements. This can be achieved using a variety if mechanisms such as static configuration or the activation of a service discovery mechanism. The exact specification of how this provisioning is achieved is out of scope. 4.2. SF Symmetry Some SFs require both directions of a flow to traverse. Some service function chains require full symmetry. If a SF (e.g., stateful firewall or NAT) needs both direction of a flow, it is the SF instantiation that needs both direction of a flow to traverse, not the abstract SF (which can have many instantiations spread across the network). 4.3. Pre-deploying SFCs Enabling service function chains should preserve some deployment practices adopted by Operators. Particularly, installing a service function chain (and its associated SFPs) should allow for pre- deployment testing and validation purposes (that is a restricted and controlled usage of such service function chain (and associated SFPs)). 4.4. Withraw a Service Function (SF) During the lifetime of a SFC, a given SF can be decommissioned. To accommodate such context and any other case where a SF is to be withdrawn, the control plane should instruct the SFC data plane functional element about the behavior to adopt. Particularly: 1. a first approach would be to update the service function chains (and associated SFPs) where that SF is present by removing any Li, et al. Expires February 29, 2016 [Page 14] Internet-Draft SFC Control Plane August 2015 reference to that SF. Doing so avoids to induce service failures for end users. 2. a second approach would be to delete/deactivate any service function chain (and its associated SFPs) that involves that SF but install new service function chains. 4.5. SFC/SFP Operations Various actions can be executed on a service function chain (and associated SFPs) that is structured by the SFC Control & Management planes. Indeed, a service function chain (and associated SFPs) can be enabled, disabled, its structure modified by adding a new SF hop or remove an SF from the sequence of SFs to be invoked, its classification rules modified, etc. A modification of a service function chain can trigger control messages with the appropriate SFC-aware nodes accordingly. 4.6. Unsolicited (Notification) Messages Involved SFC data plane functional element must be instructed to send unsolicited notifications when loops are detected, a problem in the structure of a service function chain is encountered, a long unavailable forwarding path time is observed, etc. Specific criteria to send unsolicited notifications to a Control Element should be fine tuned by the control plane using the interface defined in Section 3.3. 4.7. SF Liveness Detection The control plane must allow to detect the liveliness of SFs of an SFC-enabled domain. In particular, it must allow to dynamically detect that a SF instance is out of service and notify the relevant Control Element elements accordingly. The liveness information may be acquired directly from SFs or indirectly from other management and control systems in the operational environment. Liveness status records for all SF instances, and service function chains (including the SFPs bound to a given chain) are maintained by the SFC Control & Management. The Classifier may be notified by the control plane or be part of the liveness detection procedure. The ability of a SFC Control Element to check the liveness of each SF present in service function chain has several advantages, including: Li, et al. Expires February 29, 2016 [Page 15] Internet-Draft SFC Control Plane August 2015 o Enhanced status reporting by the control & management planes (i.e., an operational status for any given service chain derived from liveness state of its SFs). o Ability to support various resiliency policies (i.e., bypass a node embedding an SF, use alternate node, use alternate chain, drop traffic, etc.) . o Ability to support load balancing capabilities to solicit multiple SF instances that provide equivalent functions. Because a node embedding a SF can be responsive from a reachability standpoint (e.g., IP level) while the function its provides may be broken (e.g., a NAT module may be down), additional means to assess whether an SF is up and running are required. These means may be service-specific. 4.8. Monitoring & Counters SFC-specific counters and statistics must be provided using the interfaces defined in Section 3.3. These data include (but not limited to): o Number of flows ever and currently assigned to a given service function chain and a given SFP. o Number of flows, packets, bytes dropped due to policy. o Number of packets and bytes in/out per service function chain. o Number of flows, packets, bytes dropped due to unknown service function chain (this is valid in particular for a SF node). 4.9. Validity Lifetime SFC instructions communicated via the various interfaces introduced in Section 3.3 may be associated with validity lifetimes, in which case classification entries will be automatically removed upon the expiry of the validity lifetime without requiring an explicit action from a Control Element. Lifetimes are used in particular by an SFC data plane element to clear invalid control entries that would be maintained in the system if, for some reason, no appropriate action was undertaken by the control plane to clear such entries. Both short and long lifetimes may be assigned. 4.10. Considerations Specific to the Centralized Path Computation Model This section focuses on issues that are specific to the centralized deployment model (Section 3.2). Li, et al. Expires February 29, 2016 [Page 16] Internet-Draft SFC Control Plane August 2015 4.10.1. Service Function Path Adjustment A SFP is determined by composing SF instances and overlay links among SFFs. Thus, the status of a SFP depends on the states or attributes (e.g., availability, topological location, latency, workload, etc.) of its components. For example, failure of a single SF instance results in failure of the whole SFP. Since these states or attributes of SFP components may vary in time, their changes should monitored and SFPs should be dynamically adjusted. Examples of use cases for SFP adjustment are listed below: SFP fail-over: re-construct a SFP with replacing the failed SF instance with another instance of the same SF. SFP with better latency experience: re-construct a SFP with a low path stretch considering the changes in topological locations of SF instances and the latency induced by the (overlay) connectivity among SFFs. Traffic engineered SFC: re-construct SFPs to localize the traffic in the network considering various TE goals such as bypass a node, bypass a link, etc. These techniques may be used for planned maintenance operations on a SFC-enabled domain. SF/SFC Load balancing: re-construct SFPs to distribute the workload among various SF instances. For more details about the use cases, refer to [I-D.lee-nfvrg-resource-management-service-chain]. The procedures for SFP adjustment may be handled by the SFC control plane as follows: o Collect and monitor states and attributes of SF instances and overlay links via the C2 interface (Section 3.3.2) and the C3 interface (Section 3.3.3). o Evaluate SF instances and overlay links based on the monitoring results. o Select SF instances to re-determine a SFP according to the evaluation results. o Replace target SF instances (e.g., in a failure or overladed) with newly selected ones. o Enforce the updated SFP for upcoming SFC traversal to SFFs via the C1 interface (Section 3.3.1) or the C2 interface (Section 3.3.2). 4.10.2. Head End Initiated SFP Establishment In some scenarios where a SFC Control Element is not connected to all SFFs in a SFC-enabled domain, the SFC control plane can send the explicit SFF-SF-sequence or SF-sequence to the SFC head-end, e.g., Li, et al. Expires February 29, 2016 [Page 17] Internet-Draft SFC Control Plane August 2015 the SFC Classifier via the C1 interface (Section 3.3.1). SFC head- end can use a signaling protocol to establish the SFF-SF-sequence based on the SF-sequence. 4.10.3. (Regional) Restoration of Service Functions There are situations that it might not be feasible for the Classifier to be notified of the changes of SFF-sequence or SFF-SF-Sequence for a given SFP because of the time taken for the notification and the limited capability of the Classifiers. If a SF has a large number of instantiations, it scales better if the Classifier doesn't need to be notified with status of visible instantiations of SFs on a SFP. It might not be always feasible for the Classifier to be aware of the exact SF instances selected for a given SFP due to too many instances for each SF, notifications not being promptly sent to the Classifier, or other reasons. This is about multiple instances of the same SF attached to one SFF node; those instances can be handled by the SFF via local load balancing schemes. Regional restoration can take the similar approach as the global restoration: choosing a regional ingress node that can take over the responsibility of installing the new steering policies to the involved SFFs or network nodes. Typically, the regional ingress node should be: o on the data path of the flow of the given SFC; o in front of the relevant SFFs or network nodes that are impacted by the change of the SFP; o capable of encoding the detailed SFP to the Service Chain Header of data packets of the identified flow; and o capable of removing the detailed SFP encoding in data packets after all the impacted SFFs and network nodes completed the policy installation. 5. Security Considerations 5.1. Secure Communications The SFC Control Elements and the participating SFC data plane elements must mutually authenticate. SFC data plane elements must ignore instructions received from unauthenticated SFC Control Elements. The credentials details used during authentication can be used by the SFC control plane to decide whether specific authorization may be granted to a Service Function with regards to Li, et al. Expires February 29, 2016 [Page 18] Internet-Draft SFC Control Plane August 2015 some specific operations (e.g., authorize a given SF to access specific context information). In case multiple SFC data plane elements are embedded in the same node, the authentication mechanism may be executed as a whole; not for each instance. A SFC data plane element must be able to send authenticated unsolicited notifications to a SFC Control Element. The communication between a Control Element and SFC data plane elements must provide integrity and replay protection. An SFC Control Element may instruct a Service Function to include specific security token(s) that may be used to decrypt traffic upstream. The security token may be supplied by the SFC control plane or by an authorized Service Function (e.g., TLS proxy). The exact details on how authorization is granted to a specific SF, including via a control plane interface, should be specified. A Service Function must by default discard any action from a SFC Control Element that requires specific right privileges (e.g., access to a legal intercept log, mirror the traffic, etc.). 5.2. Pervasive Monitoring The authentication mechanism should be immune to pervasive monitoring [RFC7258]. An attacker can intercept traffic by installing classification rules that would lead to redirect all or part of the traffic to an illegitimate network node. Means to protect against attacks that would lead to install, remove, or modify classification rules must be supported. 5.3. Privacy The SFC control plane must be able to instruct SFC data plane elements about the information to be leaked outside an SFC-enabled domain. Particularly, the SFC control plane must support means to preserve privacy [RFC6973]. Context headers may indeed reveal privacy information (e.g., IMSI, user name, user profile, location, etc.). Those headers must not be exposed outside the operator's domain. 5.4. Denial-of-Service (DoS) In order to protect against denial of service that would be caused by a misbehaving trusted SFC Control Element, SFC data plane elements should rate limit the messages received from an SFC Control Element. Li, et al. Expires February 29, 2016 [Page 19] Internet-Draft SFC Control Plane August 2015 5.5. Illegitimate Discovery of SFs and SFC Control Elements Means to defend against soliciting illegitimate SFs/SFFs that do not belong to the SFC-enabled domain must be enabled. Such means must be defined in service function discovery and SFC Control Element discovery specification documents. 6. IANA Considerations This document does not require any IANA actions. 7. References 7.1. Normative References [I-D.ietf-sfc-architecture] Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", draft-ietf-sfc-architecture-11 (work in progress), July 2015. 7.2. Informative References [I-D.ietf-opsawg-firewalls] Baker, F. and P. Hoffman, "On Firewalls in Internet Security", draft-ietf-opsawg-firewalls-01 (work in progress), October 2012. [I-D.ietf-sfc-dc-use-cases] Surendra, S., Tufail, M., Majee, S., Captari, C., and S. Homma, "Service Function Chaining Use Cases In Data Centers", draft-ietf-sfc-dc-use-cases-03 (work in progress), July 2015. [I-D.ietf-sfc-use-case-mobility] Haeffner, W., Napper, J., Stiemerling, M., Lopez, D., and J. Uttaro, "Service Function Chaining Use Cases in Mobile Networks", draft-ietf-sfc-use-case-mobility-04 (work in progress), July 2015. [I-D.lee-nfvrg-resource-management-service-chain] Lee, S., Pack, S., Shin, M., and E. Paik, "Resource Management in Service Chaining", draft-lee-nfvrg-resource- management-service-chain-01 (work in progress), March 2015. Li, et al. Expires February 29, 2016 [Page 20] Internet-Draft SFC Control Plane August 2015 [I-D.lee-sfc-dynamic-instantiation] Lee, S., Pack, S., Shin, M., and E. Paik, "SFC dynamic instantiation", draft-lee-sfc-dynamic-instantiation-01 (work in progress), October 2014. [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, DOI 10.17487/RFC3022, January 2001, <http://www.rfc-editor.org/info/rfc3022>. [RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z. Shelby, "Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations", RFC 3135, DOI 10.17487/RFC3135, June 2001, <http://www.rfc-editor.org/info/rfc3135>. [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, April 2011, <http://www.rfc-editor.org/info/rfc6146>. [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- Stack Lite Broadband Deployments Following IPv4 Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011, <http://www.rfc-editor.org/info/rfc6333>. [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, DOI 10.17487/RFC6973, July 2013, <http://www.rfc-editor.org/info/rfc6973>. [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014, <http://www.rfc-editor.org/info/rfc7258>. [RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for Service Function Chaining", RFC 7498, DOI 10.17487/RFC7498, April 2015, <http://www.rfc-editor.org/info/rfc7498>. Li, et al. Expires February 29, 2016 [Page 21] Internet-Draft SFC Control Plane August 2015 Appendix A. RSP-related Considerations NOTE: This section records some contributions proposed by L. Dunbar and A. Malis, but have not been discussed yet among authors. A.1. Encoding the Exact SFF-SF-sequence in Data Packets Encoding the exact RSP in every packet has the benefit and the issues associated with source routing. This approach may not be optimal when the SFP doesn't change very frequently, as in minutes or hours. There are contexts that it might not be feasible for the head end Classifier to be notified of the changes of SFF-sequence or SFF-SF- Sequence for a given SFP because of the time taken for the notification and the limited capability of the Classifier nodes. A.2. Fully Controlled SFF-SF-Sequence for a SFP This section describes the information that can be exchanged over C2 interface (Section 3.3.2) when the SFC Control Element explicitly passes the steering policies to all SFFs for the SFF-SF-Sequence of a given SFC. In this model, each SFF doesn't need to signal other SFFs for the SFP. Suppose the SFC ID for this SFP is "yellow", an example of policy to "sff-a" is depicted in Figure 2 (for illustration proposes) Matching | Action ----------------------------------------+------------------------- SFC ID = "yellow" & ingress = sffx-port | next-hop: "sf2" & VID SFC ID = "yellow" & ingress = sf2-port | next-hop: "sf3" & VID SFC ID = "yellow" & ingress = sf3-port | next-hop: sff-b Figure 2: Example of Traffic Steering Policy to a SFF node The SFF nodes may not be directly adjacent to each other. They can be interconnected by tunnels, such as GRE, VxLAN, etc. SFs are attached to a SFF node or SFC Proxy node via Ethernet link or other link types. Therefore, the steering policies to a SFF node for service function chain depends on if the packet comes from previous SFF or comes from a specific SF, i.e., the SFC Forwarding Policy Table entries have to be ingress port specific. There are multiple different steering policies for one flow within one SFF and each set of steering policies is specific for an ingress port. The semantics of traffic steering rules can be "Match" and "Action", similar to the "route" described in [I-D.ietf-i2rs-rib-info-model]. The "match" and "action" for distinct ports can be different. The Li, et al. Expires February 29, 2016 [Page 22] Internet-Draft SFC Control Plane August 2015 matching criteria for SFF can be more sophisticated. For example, the matching criteria could be any fields in the data packets: o Ingress port o Destination MAC address o Source MAC address o VLAN_id, o Destination IP address o Source IP address o Source port number o Destination port number o DSCP o Packet size, etc., or any combination thereof. A SFF node may not support some of the matching criteria listed above. It is important that SFC control plane can retrieve the supported matching criteria by SFF nodes. The "Actions" for traffic steering could be to steer traffic to the attached service function or SF instantiations via a specific port. The "Actions" to SFC Proxy may include a method to map the SFC Identifier carried in the packet header to a locally significant link identifier, e.g., VLAN-ID, and a method to construct and encapsulate the SFC header back to the packets when they come back from the attached SFs. This approach does not require using an end-to-end signaling protocol among Classier nodes and SFF nodes. However, there may be problems encountered if SFF nodes are not updated in the proper order or not at the same time. For example, if the SFF "A" and SFF "C" get flow steering policies at slightly different times, some packets might not be directed to some service functions on a chain. Acknowledgments This document is the result of merging with [I-D.lee-sfc-dynamic-instantiation]. The authors would like to thank Shibi Huang and LAC Chidung for the review and comments. The text about the semantic of a context information is provided by Dave Dolson. Li, et al. Expires February 29, 2016 [Page 23] Internet-Draft SFC Control Plane August 2015 Contributors Many thanks to the following people for contributing text to the document: o tbc Authors' Addresses Hongyu Li Huawei Huawei Industrial Base,Bantian,Longgang Shenzhen China EMail: firstname.lastname@example.org Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China EMail: email@example.com Yong(Oliver) Huang Huawei Huawei Industrial Base,Bantian,Longgang Shenzhen China EMail: firstname.lastname@example.org Mohamed Boucadair (editor) France Telecom Rennes 35000 France EMail: email@example.com Li, et al. Expires February 29, 2016 [Page 24] Internet-Draft SFC Control Plane August 2015 Christian Jacquenet France Telecom Rennes 35000 France EMail: firstname.lastname@example.org Walter Haeffner Vodafone D2 GmbH Ferdinand-Braun-Platz 1 Duesseldorf 40549 DE EMail: email@example.com Seungik Lee ETRI 218 Gajeong-ro Yuseung-Gu Daejeon 305-700 Korea Phone: +82 42 860 1483 EMail: firstname.lastname@example.org Ron Parker Affirmed Networks Acton MA 01720 USA EMail: email@example.com Linda Dunbar Huawei Technologies USA EMail: firstname.lastname@example.org Andrew Malis Huawei Technologies USA EMail: email@example.com Li, et al. Expires February 29, 2016 [Page 25] Internet-Draft SFC Control Plane August 2015 Joel M. Halpern Ericsson EMail: firstname.lastname@example.org Tirumaleswar Reddy Cisco Systems, Inc. Cessna Business Park, Varthur Hobli Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560103 India EMail: email@example.com Prashanth Patil Cisco Systems, Inc. Bangalore India EMail: firstname.lastname@example.org Li, et al. Expires February 29, 2016 [Page 26]